Sanding drum



Feb. 19,1935. I w WALKER 1,992,105

SANDING DRUM Filed Dec. 8, 1935 INVENTOR. AV ERY W. WALKER I ATTORNEY.

' Patented Feb. 19, 1935 PATENT OFFICE SANDING DRUM REESSUED Avery W.Walker, Niagara Falls, N. Y., assignor to The Carborundum Company,Niagara Falls, N. Y., a corporation of Pennsylvania Application December8,1933, Serial No. 701,489 8 Claims. (01. 51-194) This invention relatesto sanding and polishing abrasive drums of the general type in which thedrums are provided with removable and replaceable abrasive bands orbelts around their periphcry, and relates particularly to drums having anew and improved mechanism for maintaining a predetermined tension onthe bands while in use.

The object of the invention is to provide a new and improved drum of thecharacter described.

It is necessary in using this type of drum to keep the band tight.Elongation of the band is the result of two forces, namely that ofcentrifugal force upon the mass of the belt itself, which is ofconsiderable magnitude at the high speeds at which this type of drum isused, and that of an elongation stress caused by resistance of the workitself. These combined stresses cause an elongation sufficient toproduce a loop-like locus ahead of the point of contact of the drum withthe work. This constant flexing of the band tends to crack it and loosenthe abrasive material, shortening the effective life of the band.Furthermore, such a loop is detrimental to the character of the polishedsurface. The loop changes in shape and resiliency as it approaches theslot through which the ends of the band are threaded, causing unevenpressure on the work and resulting in ridges on the surface beingpolished.

Devices have been developed for adjusting the polishing operation. Theoperation of these devices necessitated stopping the drum and'making amanual adjustment. This method only partially accomplishes the desiredresult and is ob- 35 jectionable due to the loss of time involved.

Means for automatically maintaining a desired tension on the band duringoperation have been somewhat unsatisfactorily accomplished by others inthe past. The necessity for maintaining 40 perfect balance of the drumat all times precludes those devices in which the center of gravityshifts during progressive absorption of band elongation, and previousattempts to secure this balance have led to the use of relatively wideslots in the drums in order to accommodate various mechanisms.

' In known devices of this sort the degree of tension is fixed by theinstallation of springs of known elasticity and can only be varied bydisassembling the drum, changing the springs, lengthening or shorteningthe springs, or by an internal adjustment of the spring supportingmembers.

-To obtain good results in the. use of drums of this type it isnecessary to have substantially perfect balance and a relatively narrowfacial interruption at the slot. A very-slight out of balance tensionfrom time to time during the grinding or condition, no matter how rigidthe machine and work, causes high and low spots in the finish of thework and excessive vibration with consequent wear on the bearings whichin turn allows increased vibration creating a vicious cycle ofconstantly increasing detrimental effect. A relatively wide facialinterruption due to a wide slot causes marks on the work due to periodicinterruptions of contact and to a bouncing effect caused by the impactof the leading edge of the slot. It is clearly seen, then, that thenarrower the slot orfacial gap, the more constant is the contact,reducing the bouncing effect and reducing the non-operative interruptionto a minimum.

This invention successfully overcomes these difiiculties by' makingpossible a drum of constant balance having a relatively narrow facialinterruption, an improved gripping mechanism and a simplified designenabling a quick change of belts.

Figure 1 is a side elevation, partly in section, of an assembled drum.

Figure 2 is a'sectional view through II II.

Figure 3 is a sectional view through l1I-III showing in elevation one ofthe innermembers 2 upon which are mounted parts of the clamping andtensioning mechanism.

Figure 4 is an end view of an assembled drum with the cover plateremoved showing the assembled tensioning mechanism.

Figure 5 is a sectional view of the" tensioning idler and grippingmechanism showing a band in place and under tension.

Referring to the drawing in which like numbers refer to the same partsin all views, the body 1 is a specially shaped cylindrical body adaptedto be mounted on a shaft in any preferred manner, and to be rotatedtherewith or thereon at any desired speed. This body is provided withspokes extending longitudinally, preferably, be-' yond that part whichis to be surfaced by the coated abrasive. This construction eliminatesany bulging or expanding of the central portion of the drum which'wouldcause uneven surfacing of wide material. The fillets at the junction ofthe spokes with the outer rim have a curvature of substantiallyparabolic shape. This construction is specifically intended to keep thedrum surface truly cylindrical at all speeds so as to eliminate thebumping effect often noticed in wheels of this type which is due to asurface distortion from centrifugal force. This design is the strongestfor its weight and has been found entirely free from this defect. Thecylinder is provided with a longitudinal slot for applying the coatedabrasive as shown. Opposite the slot sufficient material is removed toprovide for balancing.

Balanced end cover plates are provided at both ends of the drum, theirchief function being merely to protect the inner mechanism frommechanical injury and from collection of foreign matter during theoperation of the drum. These covers are provided with holes of suitablesize so disposed as to permit the operator to insert a socket wrench totighten the clamping cams when installing a new band.

Figure 4 shows the tensioning and tension adjusting mechanism. Thisassembly is duplicated at the other end of the drum allowing for ad--justments from either end. The transfer shaft 4 turns in bearings in theinner members 2 and is provided with worm gears 5 which mesh withsimilar worms 6 on the tension adjusting shafts 3 at both ends of thedrum. These tension adjusting shafts 3 are also provided with worm gears7 in mesh with the large worm gears 8. When the tension adjusting shaft3 is turned, movement is transmitted through the worm gears 8 which aresecured to the tension adjusting members 9. When these members 9 areturned about the main axis in a counter-clockwise direction, compressionof the springs 23 is effected, and pressure is thereby resilientlytransmitted to the tension idler bar support members 12 which are freeto rotate and thence to the tension idler bar 10. Due to inherentcharacteristics of worm gears, they can be cut with such pitches thattheir movement is practically irreversible and thereby provide anautomatic locking'effect holding the springs under the desiredcompression. The transfer shaft 4 provides for equal and simultaneousadjustment at both ends of the drum.

Diametrically opposite the tension idler bar 10 is a dummy bar 11 whichis merely a counter-balance for the tension idler bar 10. Both of thesebars are supported at opposite ends of the tension idler bar supportmembers 12. The tension adjusting shafts 3 and their worm gears arecounterbalanced by the dummy bars 13. The cam shafts 15 and the clampbacking 16 are counter-balanced by the dummy bars 17, the transfer shaft4 and the dummy bar 14. Such duplicated parts as the compression springsand their brackets are diametrically disposed so as to effect perfectbalance.

It is necessary to form the cams 18 with counter-balancing faces 19 inorder that the center of gravity of the cams may not shift whendifferent thicknesses of belts are used.

It will be seen that this design provides a drum in which each of theassembled units functions 'in balance with another unit and each has itscenter of gravity axially situated at all adjustments when-assembled.This construction provides dynamic and static balance for the assembleddrum which condition is essential as explained above.

The tension idler bar 10 is provided with a covering of resilientmaterial such as rubber. This assures uniform tension on the belt eventhough there may be slight local variations in the belt which wouldotherwise result in uneven tension if the tension bar had anon-resilient surface. When wide drums are covered with a wide belt outfrom coated paper or cloth these variations are prevalent and unless thetension bar has a resilient surface to take up these irregularities,

- slack portions of the abrasive covered material cause an irregularsurface on the work being finished.

The ends of the shafts 3 extend into recesses in the cylinder beyondthat portion covered with the belt as shown at 21, and are machined forthe application of a socket wrench or other tool. To face the drum witha belt a tool is used to turn one of the tension adjusting shafts 3until the tension idler bar 10 is directly under the slot in the maincylinder. The wrench is then used to turn the cam shafts 15, opening thecams and creating gaps between the cam faces 20 and the clamp backing16. One end of the band is inserted through the slot and in between thecam shaft and clamp backing under the leading edge of the slot, beingthe one to the right in the accompanying drawing. The right hand camshaft is then turned in a clockwise direction clamping the belt securelybetween the cams and backing member. The belt is then wrapped tightlyaround the drum on which is cemented a padding of felt or otherresilient material 22 and the remaining end inserted through the slot,past the tension idler bar 10 and into clamping position in the otherclamp, which is then tightened by turning the left-hand cam shaft in acounter-clockwise direction. The cam faces are so shaped that tension onthe belt tends to rotate them in the direction which increases thegripping effect. The tension adjusting shaft 3 is then turned until thetension bar 10 presses against the belt the desired degree. Thisarrangement is clearly depicted in Figure 5.

Although a specific example of an application of this invention isillustrated and described, modifications will be obvious to thoseskilled in this art, and protection of this invention is sought 1 withinthe scope of the annexed claims.

I claim:

1. An abrasive drum comprising in combination a cylinder adapted to becovered with an abrasive coated belt, means for securing the ends ofsaid belt within the cylinder, means for effecting and maintaininganydesired degree of tension on said belt, and automatic means formaintaining the said drum in static and dynamic balance at all positionsof the said securing means and the said tension means.

2. An abrasive drum comprising in combination a cylinder adapted to beexternally covered with an abrasive coated belt, externally operatedmeans for gripping the ends of said belt within the cylinder, externallyoperated means foreffecting and maintaining any desired degree oftension on the belt, and automatic means for maintaining the said drumin static and dynamic balance at all positionsof the said gripping meansand the said tension means.

3. An abrasive drum comprising in combination a cylinder adapted to beexternally surfaced with a replaceable abrasive coated belt, externallyoperated means for gripping the ends of said belt within the cylinder,externally operated means for effecting and maintaining any desireddegree of tension on said belt, and automatic means .for maintaining thesaid drum in static and dynamic balance at all positions of the saidgripping means and the said tension means, said gripping means and saidtensioning means being adapted to be operated independently of eachother.

4. An abrasive drum comprising in combination a cylinderadapted to beexternally surfaced with an abrasive coated material, means for grippingthe ends of said material within the cylinder, and automatic means formaintaining the said drum in static and dynamic balance at all positionsof the said gripping means, said gripping means being operable by a toolapplied from the outside of the drum.

5. An abrasive drum comprising in combination a cylinder adapted to besurfaced with'an abrasive coated material, and means located within thecylinder for effecting and maintaining any desired degree of tension onsaid material, automatic means for maintaining the said drums in staticand dynamic balance at all positions of the said tension means, saidtensioning means being operated by a tool such as, for example, a-

wrench applied from the outsidevof the drum.

6. An abrasive drum comprising in combination a cylinder adapted to beexternally covered with an abrasive coated belt, means for causing theends of the belt to be gripped within the cylinder by the application ofa tool from the outside of the drum, means for effecting and maintainingany desired degreeof tension on the belt by the application of a toolfrom the outside of the drum, and automatic means for maintaining thesaid drum in static and dynamic balance at all positions of the saidgripping means and the said tension means.

'7. In an abrasive drum adapted to be externally covered withreplaceable abrasive coated belts, an internal belt gripping devicecomprising a longitudinal fixed member, two rotatable cam shaped membersso disposed whereby rotation of one cam member in one direction effectsa closure of the gap between it and the fixed member and rotation of theother cam member in the opposite direction effects a closure of the gapbetween it and the fixed member while reversal of these directions ofrotation effects openings of said gaps, said rotatable cam membershavingv their centers of gravity situated on their axes of rotation andall parts of the said belt gripping device being counter-balanced withrespect to the axis of the drum, and means to automaticallycounterbalance the said belt gripping device with respect to the axis ofthe drum at all positions of the said device.

8. In an abrasive drum adapted to be extere nally covered with areplaceable abrasive coated belt having its ends gripped within thedrum, an internal belt tensioning device co-axial with the drum andcomprising two or more supporting members simultaneously rotatable aboutthe axis of the drum, a longitudinal member whose axis is parallel tothe axis of the drum supported by said rotatable supporting members andso situated as to be contactable with the surface of the belt on a linebetween its entrance to the drum and a gripped end, means to efiect andmaintain said contact to a desired degree of pressure by the applicationof a tool from the outside of the drum, and means to automaticallycounterbalance said cont-acting member with respect to the axis of thebelt tensioning device at all positions of the said device.

AVERY W. WALKER.

